The invention relates to multi-layer highly crystalline polymer films having improved surface characteristics. The invention also relates to a method of improving the surface characteristics of highly crystalline thermoplastic resin films.
Polymeric films, useful for applications such as packages and other forms of wrapping, inherently possess certain characteristics which hinder the easy handling of the film during its use. In order to overcome these characteristics the film surface has to be modified by the provision thereon of materials calculated to improve the film handling. For example, slip agents, anti-blocking agents, anti-static agents, etc. are provided on the surface to overcome the inherent, undesirable characteristics of the resin in film form. It is common practice with films such as polypropylene to incorporate into the resin material certain slip agents so that during formation of the polypropylene film the slip agent will come to the surface or bloom and thus be available to form a low coefficient of friction surface thereby improving the handling of the film. Unfortunately, it has been discovered that for certain polymer films the amount of additive released to the surface by exudation or blooming is not always in an effective amount.
Oriented highly stereoregular polypropylene film has become a useful and widely accepted packaging film because of its good moisture barrier, stiffness, high strength, and good optical properties. This material, however, is an example of an excellent film which exhibits poor handling characteristics. It appears that as the degree of stereo-regularity increases the quantity of surface modifying additive exuded to the surface decreases.
Its an object of the present invention to provide a multi-layer film structure having an effective amount of surface modifying material on at least one surface thereof.
Another object of the instant invention is to present a process for improving the surface characteristics of a polymer film of comparatively high stereo regularity.